Unique Nature

Boulder clay

The most prominent element in the Holtingerveld is the Havelterberg. This hill is 19 metres high and was formed by glacial processes in the Saale Cold Period, the second last ice age, some 150,000, just like the Bisschopsberg and the Woldberg. The ice pushed tonnes of material in front of it and pulverised it into a thick layer of boulder clay. After the ice melted, this mess was what was left behind.

Over the following centuries, the wind blew a layer of sand over the clay, of varying thickness. Boulder clay can be found almost everywhere in the province of Drenthe. At the Havelterberg this layer of clay is over ten metres in thickness and breaks through the surface. Boulder clay has a dense structure and consists of very diverse material with clay, sand, gravel and stones. The largest stones have been used by the people of the funnelbeaker culture, who built the dolmens. On the North side of the Havelterberg, there is another boulder clay ridge, however this one is much lower and you’ll probably not notice it. On top of this ridge, the stretched-out village of Wapserveen is situated.

The boulder clay contains many minerals, which has caused a very wide variety of plants to grow on the Havelterberg. The combination of vegetation growing on the Havelterberg cannot be found anywhere else in the Netherlands. More rare species of plants are growing here than anywhere else in Drenthe.

From the dolmens, there is a ‘steep’ path that takes you up the mountain. The path crosses a dry moor with heather and wavy Hair-grass, like many other moors in Drenthe. The landscape on top of the mountain is very different altogether. The thick layer of clay is quite impermeable for water and as a consequence, the ground is much wetter here than on the slopes of the hill.

The minerals from the clay and the water create the perfect conditions for all kinds of special plants. These “mountain pastures” are home to all kinds of rare plants such as the bitter vetch, the zigzag clover, the salad burnet, slender St John’s-Wort and moonworts. Staatsbosbeheer takes care of these valuable pastures by mowing them once a year and by having cattle and sheep graze on them outside the flowering season. This way the wealth of plant species is maintained.